The invention relates to an arrangement and a method for measuring a temperature, in particular for high-power semiconductors.
The high-power switching of electrical consumers with elements such as mechanical relays is known. However, these are only conditionally reliable and are sensitive, in particular to mechanical stresses. Integrated semiconductor switches are increasingly used for the high-power switching of electrical consumers since these semiconductor switches have a higher reliability and a lower sensitivity relative to mechanical vibrations. However, these components have the disadvantage that they are more sensitive than mechanical relays to electrical and/or thermal overloads because of their p/n barrier layers.
A continuous operation at high temperatures, near the maximum permissible barrier layer temperature, accelerates the degradation of semiconductor component. In addition, the sensitivity to other overload conditions is increased. Excessive current endangers the semiconductor component in two ways. On the one hand, the metal coating and/or the bond-wire system can be damaged if the permissible current densities are exceeded. On the other hand, there is danger that the excessive current will lead to an extremely sharp increase in the loss power, thus causing the component to fail if the maximum barrier layer temperature is exceeded.
Different types of overload protection devices for semiconductors are known. Essentially, the protection focuses on monitoring the barrier-layer temperature (on-chip temperature measuring), as disclosed in the German Patent 41 22 653 C2 or the monitoring of the load current for the power semiconductor, as known from the German Patent 43 20 021 A1.
With monolithically integrated power semiconductor switches, so-called smart power circuits, a sensor is frequently used to monitor the temperature. This sensor is thermally connected to the semiconductor barrier layer that switches the main current. The design disclosed in the German Patent Specification 41 22 653 C2 provides that some of the switching cells in the switching arrangement are designed to be particularly weak and that the barrier layer temperature of the switching arrangement is measured directly at those locations. Thus, the highest component temperature is measured at these artificially created weak locations. Once a maximum local component temperature is exceeded, the switch is turned off without this causing a thermal overload for the other cells in the switch. This arrangement, however, poses high requirements with respect to technology, e.g. by requiring additional contact connections for the temperature sensor. The alternative of determining the component temperature at a location far from the barrier layer, e.g. on the housing, leads to intolerable time delays during a sudden temperature increase as a result of the great distance to possibly thermally stressed barrier layers. In the final analysis, it leads to the destruction of the barrier layer.
It is the object of the invention to use a simple method for measuring the outside temperature of a component, particularly of a non-contacting switch.
This object is solved according to the invention by the features in the independent claims. Modified and advantageous embodiments follow from the additional claims and the description. The invention makes it possible to determine and monitor the component temperature with less expenditure.
The invention starts with the premise of providing overload protection for the active zone J or zones J to be controlled of a switch having a load circuit and a control circuit by using a combination of residual voltage monitoring and temperature monitoring. The overload protection is further improved with the temperature-measuring arrangement according to the invention, as well as an advantageous compensation method.
The control circuit is dimensioned such that the thermal resistances are taken into consideration for limiting the maximum load current flowing in the switch. These thermal resistances hinder the heat discharge between the active zone and/or the active zones J inside the switching body, which are particularly affected by the loss power and present an obstacle for a temperature sensor at the outside of the switching element. It is thus achieved that the maximum permissible temperature at the active zone J to be controlled of the switch cannot be exceeded.
The invention is preferably used for switches encumbered with loss power and is particularly preferred for MOSFET switches.
The fact that switches of this type can be utilized over a broader power range than is normally possible, owing to their dimensional layout, is an advantage. In contrast to the prior art, the dimensional layout no longer is a xe2x80x9cworst casexe2x80x9d estimation. The maximum load current in the switch is reliably limited. It is therefore possible to operate the switch continuously near the maximum temperature, without risking the destruction of an active zone J to be controlled in the switching body through short, undetectable or only delayed detectable temperature peaks. There is no need for a quick temperature measurement in order to monitor the temperature, in particular temperature peaks, at the active zone J, so that cheap, simple and even slower temperature measuring methods can be used.
Another advantage is that the dimensional layout of the switch/control circuit makes it possible to measure the switch temperature not near the barrier layer, but more usefully near the housing, which simplifies the measuring arrangement. According to the invention, a bipolar transistor or a diode is used in that case for the temperature measuring.
According to the invention, one of the electrical contacts of the temperature sensor must be arranged electrically as well as thermally at least indirectly at the switch and/or the switch housing. Particularly suited are transistors or diodes. It makes sense if these have essentially planar contacts, which permit a particularly good thermal connection to the switch. An especially preferred arrangement is the direct hook-up of the collector terminal of a preferably used bipolar transistor to the drain of a preferably used MOSFET switch. Together with the dimensional layout of the switch/control circuit according to the invention, this simple and cheap temperature-measuring arrangement represents a further simplification and improvement of the overload monitoring.
The temperature measuring point can be, for example, a conductive track, a barrier layer, a housing or the like for one or several switches to be monitored. This advantageous type of temperature measuring is suitable for different components and is not limited to the use of semiconductor switches.
A particularly advantageous modification of the invention consists in compensating the temperature dependence of the switching threshold of the switch/control circuit. The temperature in that case can be measured near the barrier layer or far from the barrier layer. The method according to the invention therefore can be used advantageously not only for the preferred arrangement, but also for switches, particularly semiconductor switches, where at least indirectly, the barrier layer temperature itself is monitored.